;; Name         : John Doe
;; GT Number    : gti999z
;; HW           : HW2
;; Course       : cs1321
;; Instructor   : Lerner
;; Lecture Time : 6:00 pm
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; <1>
;; Data Analysis & Definitions:
(define PI 3.14)

;; Contract: area-of-disk : number -> number

;; Purpose: to compute the area of a disk with a
;; given radius

;; Examples: 
;; (area-of-disk 3) should produce 28.26
;; (area-of-disk 1) should produce 3.14

;; Template: 
;; <required as of HW6>
;;

;; Definition:
(define (area-of-disk radius)
  (* PI (* radius radius)))
  
;; Tests:
(area-of-disk 1)
;; expected value
3.14

(area-of-disk 3)
;; expected value
28.26

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; <2>
;; Data Analysis & Definitions:
;; <not required for this function>

;; Contract: area-of-ring : number number -> number

;; Purpose: to compute the area of a ring whose radius
;; is outer and whose whole has a radius of inner.

;; Examples: 
;; (area-of-ring 5 3) should produce 50.24
;; (area-or-ring 7 6) should produce 40.82

;; Template:
;; <required as of HW6>
;;

;; Definition:
(define (area-of-ring outer inner)
  (- (area-of-disk outer)
     (area-of-disk inner)))

;; Tests:
(area-of-ring 5 3)
;; expected value
50.24

(area-of-ring 7 6)
;; expected value
40.82